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 Just Accepted

This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.


Population structure and biology of shortfin mako Isurus oxyrinchus in the Southwest Indian Ocean

Johan Groeneveld, Geremy Cliff, Sheldon Dudley, Alan Foulis, Jorge Santos, Sabine Wintner

Abstract

The population structure, reproductive biology, age and growth, and diet of shortfin makos caught by pelagic longliners (2005-2010) and bather protection nets (1978-2010) in the Southwest Indian Ocean were investigated. The mean fork length of makos caught by longliners decreased from east to west, with the smallest individuals occurring near the Agulhas Bank edge, in June to November. Nearly all makos caught by longliners were immature, with equal sex ratio. Makos caught in nets were larger, males were more frequent, and 93% of males and 55% of females were mature. Age was assessed from band counts of sectioned vertebrae, and a von Bertalanffy growth model fitted to sex-pooled length-at-age data predicted a L0 of 90 cm, L∞ of 285 cm and k of 0.113 y-1. Males matured at 190 cm, aged 7 y, and females at 250 cm, aged 15 y. Litter sizes ranged from nine to 14 pups, and the presence of gravid females in nets suggested that some pupping occurred in shelf waters. Teleosts (mainly Trachurus capensis) occurred in 84% of stomachs collected on longliners, whereas elasmobranchs (63.5%) were most common in samples collected from nets, followed by teleosts (43.1%) and cephalopods (36.5%). Larger prey size may be a factor that attracts large makos to coastal waters.

MF13341  Accepted 01 May 2014
 
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